Process of reclaiming waste polychloroprenes



Patented Mar. 7, 1944 PROCESS OF BIOLAIMI'NG POLYCHLOBOPRENE .WASTE 8 Walter G. Kirby and Leo a. Steinle, Nau'gatuoku Com, asslgnors to United States Rubber Company, New York, N. Y.. acorporation of New Jersey No Drawing. Application January 18, 1942.

Serial No. 427,024

1'1 Claims. (01. zoo-s) This invention relates to a process of reclaiming elastic polymerized ch1oro-2-butadlene-L3 in its various forms, hereinafter referred to for convenience as polychloroprene, and also the reclaimed product. 1 1

Plastic polymerized chloroprene in various forms and containing certain modifying and stabilizing agents is sold under the name of neoprene in a number of types such as E, M, G, GN, I, etc. Neoprene GN, an outstandingjmaterial, is understood to be prepared by polymerization of chloroprene in the presence of sulphur. .Neoprene I is understood to be prepared by polymerization of chloroprene and a portion of an unsaturated nitrile in the present of sulphur. When these various types of neoprene are mixed with selected modifying agents, softeners, fillers, reinforcing agents, etc., in the manner generally known to the art, and said mixtures are subjected'to a heating process, the neoprene mixture is converted from a plastic to a touch elastic material by a process generally called curing or vulcanizing. Thetougli elastic body is referred to as vulcanized neoprene. 'The vulcanization step may occur at low or high temperatures and may proceed to various degrees.

If it takes place at or near room temperature or during processing, it is referred to as scorching.

The neoprene mixtures in which scorchin3" has proceeded to even a relatively slight degree cannot besatisfactorily milled, tubed, calendered, or otherwise processed in the industry and so must be scrapped. For convenience "scorched" and fully vulcanized elastic neoprene mixtures or products made from such mixtures. will be referred to herein as vulcanized neoprene.-

The art of the reclaiming of vulcanized ordinary rubber scrap is well-known. In all of the economical methods for reclaiming scrap rubber, that are in commercial use today, high temperatures are used. These elevated temperatures which range from approximately 300 F. to approximately 400" F. are desirable because they accelerate the reversion of vulcanization and speed up the action of so-called softening agents, and thus contribute to economical plasticization. These higher temperatures are also desirable to accelerate and promote the rapid destruction of fibre where it is present. Because of these facts,

equipment that will accommodate these higher ized'neoprene it becomes harder and is said to be further vulcanized. Therefore, one of the great difficulties in attempting to reclaim scrap vulcanized neoprene is the fact that as the temperature is raised during the process to accelerate the action of oils and softening agents in plasticizing or otherwise breaking down the polymer to a plastic state, there occurs during the same I period a gradual further-polymerizing and hardening of the neoprene, due to these temperatures,

which counteracts any plasticizing effect accomplished. For this reason, processes that have been recommended to date for reclaiming scrap vulcanized neoprene have been limited to low temperatures. At low temperatures it is difllcult to get sufllcient softening action from softening agents, without using prejudicially excessive amounts.

Since high temperatures will soften ordinary vulcanized rubber scrap and .will harden vulcanized neoprene scrap it is apparent that the usual rubber reclaiming methods such as the high temperature digester-alkali or digester zinc chloride processes or the high temperature heater" process cannot be used to reclaim combinations or mixtures oi these scraps. This fact has been a source of considerable concern among scrap rubber reclaimers because the introduction of neoprene into rubber articles such as for example an automobile tire having a neoprene tread and a rubber carcass or a rubber gasoline hose having a neoprene inner lining would cause this type scrap to become valueless for further reclaiming use. Also the accidental mixing of neoprene scrap with rubber scrap would destroy the rein the same vessel mixtures of scrap vulcanized rubber and scrap vulcanized neoprene. as well as to'reclaim scrap containing combinations of rubher and neoprene. A further object is to provide a method of reclaiming vulcanized neoprene that will allow use of the same equipment that is regularly' used for reclaiming rubber, thus permitting present established rubber reclaiming plants to temperatures has become standardized and is now in'use throughout the rubber. reclaiming industry.

Neoprene is different from rubber in that it does not combine with sulphur to bring about vulcanization and does not'undergo reversion of vulcanization through the'medium of heat, to change it from an elastic to a plastic form. On the contrary when heat and especially the higher temperatures referred to. are applied to vulcan the following description.

reclaim this product with no additional cost for equipment. Other objects will be apparent from We have discovered that sugars. such as monosaccharoses and polysaccharoses, including disaccharoses, and materials which may be converted into sugars under the conditions of the reclaiming operation, such as starches..will per- ,mi-t reclaiming of scrap vulcanized neoprene .by heating the saidscrap in a suitable state of subs industry as a digester.

division with selected amounts or the reclaimin agent, and optionally with suitable oils, swelling and/or binding agents.

As examples of these reclaiming agents we may mention sucrose, dextrose, maltose, lactose, laevulose, aldohexoses, aldopentoses, ketohexoses, ketopentoses, di and polysaccharides, starches, and the various crude' sugar mixtures or solutions such as molasses, sorghum, cane syrup, corn syrup, honey, etc. The above named materials are mentioned merely as examples of the type of compounds that can be employed, and the invention is not to be understood as limited to these examples.

The proportion by weight of our reclaiming agents based on the scrap neoprene may vary depending on their strength, cost and nature of the end product reclamation desired. Generally from 2 percent to 20 percent by weight of thereclaiming agent may be used. Preferred amounts based on one of the agents such as sucrose may range from 5 to percent.

The following examples are given tion of the invention:

Example 1 Scrap vulcanized neoprene is reduced to a desired particle size and placed in an autoclave type vessel commonly known in the rubber reclaimin The scrap, together with softening oils, water, and our reclaiming agent, is sealed in the digester and heated under pressure. An illustrative batch is as follows:

Pounds in illustra- Bcrap vulcanized neoprene 10,000 Pine oil fraction 1,000 Rosin nil 1,000 Our reclaiming agent Variable Water 20,000

Another procedure is to reduce the scrap vul canized neoprene to a desired particle size, then place it in an autoclave type vessel, commonly and of a quality comparableto new commanded neoprene.

In order to further illustrate this invention we give the following examples using the previously mentioned digester type equipment.

Ex.3 Ex.4 Er.5

Scrap vulcanized neoprene Pine oil fraction lucose Viscosity of treated product as shown by a Mooney shearing plastometer Each of the above were treated by loading the Y charge into a digester and heating with steam for about 16 hours at a temperature of about 365 F.

The effectiveness of a reclaiming operation in recovering scrap vulcanized neoprene may be quantitatively shown by means of an instrument widely used for this purpose in the reclaim rub ber industry, namely, the Mooney shearing disc plastometer. This device has been described by M. Mooney in Industrial & Engineering Chemistry, an. ed. 6, 147 (1934). By means of this device the viscosity of a plastic material in shear may be readily and quantitatively measured. Experience has shown that materials with a Mooney viscosity of 50' to 160 when tested at 180 F. can

be readily and efllciently processed on standard .rubber working machinery, but that materials known in the reclaiming industry as a "heater" or devulcanizer." This process diflers from the digester process in that there is usually no agitation and there is practically no water present. The charge under treatment is in a semi-moist state rather than suspended in a solution. The

- or treatment and temperature used will vary with the type of scrap, and the period of time andtemperature may be as above specified. The

product after the usual mulling is fully reclaimed 76 all the modifying agents following batch is illustrative:

' Pounds Scrap vulcanized neoprene 3,000 Pine oil fr i 300 Rosin nil I soc reclaiming agent-.. Variable Water 120 of a very high viscosity such as 200 and over when tested at 180 F. cannot be so treated.

Example 3 represents a charge in which none 0! our reclaiming agents are used. The product has a viscosityof 196 and is considered too hard to mill. Examples 4, 5 and 6 represent charges using certain of our reclaiming agents and show that these agents have a definite reclaiming action. In these examples the viscosities range from 24 to 33 and the products can be easily milled and made useful to the rubber trade. In those examples wherein the viscosity is below 50,

the reclaiming operation would normally be modified by using less oil, less reclaiming agent, or shorter heating time, or a combination of these changes to give a viscosity in the preferred range. Proper adjustment could easily be made by one experienced in the artto give a product of the desired plasticity.

Very similar reclaiming-action will result from our reclaiming agents if used in a heater" instead of a digester. The treatment in a heater would be carried out-the same as the treatment in a digester except that 10 percent of water based on the weight of the scrap would be used instead of 200 percent.

Although for purposes of comparison, our reclaiming agents are used in the above examples with 10 parts of pine oil fractiommnd 10 parts of rosin oil, to parts or scrap vulcanized neoprene, it is to be understood that our inven-' ing agents used in the trade in the production of vulcanized neoprene products. For example, magnesia, zinc oxide, other metallic oxides, antioxidants, sulphur, accelerators, retarders, and

other ingredients which eflect the plasticity, rate of cure and/or physical properties of the vul-' canizate; also softeners, fillers and/or reinfo'rcing materials may be used.

y The mode of addition ofcur reclaiming agents is not limited in any way to the foregoing examples. We may add them at any point in the process and they may be added in any desired form, as for example, as a gas or vapor, or as a solid, or a liquid, or in solution in water or organic solvents, or in the oils, softeners, etc., which may also beused in the process.

It is evident from the above that many varia-' tions and embodiments of our invention maybe made without departing from the spirit or scope thereof.

Having thus described our invention, what we claim and desire to protect by Letters Patent is: 1. A process of reclaiming scrap containing vulcanized polychloroprene which comprises heating the same while in asub-divided condition at a temperature from about 300 F. to about 420-F. in the presence of a sugar.

2. A process of reclaiming scrap. containing vulcanized polychloroprene which comprises heating the same while in a sub-divided condition at a temperature from about 300 F. to about 420 F. in the presence of material from the group consisting of sugars and starches.

3. A process of reclaiming scrap containing vulcanized polychloroprene which comprises heating the same while in a sub-divided condition at a temperature from about 300 F. to about 420 F. in the presence of a polysaccharosa,

4; A process of reclaiming scrap containing vulcanized polychloroprene which comprises heating the same while in a sub-divided condition at a temperature from about 300 F. to about 420 F. in the presence of a disaccharose.

5. A process of reclaiming scrap containing vulcanized polychloroprene which comprises heating the same while in a sub-divided condition at a temperature from about300 F. to about 42051. in the presence of sucrose. c

6. A process of reclaiming scrap containing vulcanized polychloroprene which comprises heating the same while in a sub-divided condition at a temperature from about 300- F. to about 420 F. in the presence of a monosaccharose.

7. A process of reclaiming scrap containing K 3 a plastic state where it has a Mooney"'viscoslty substantially less than 200 when tested at.- r.

10. A process 0! reclaiming scrap containing elastic polychloroprene which comprises heating the same while in a sub-.di'videdconditi'on at'an elevated temperature in the presence of a sugar and for a time suflicient to reduce the elastic polychloroprene to a plastic state where 'ithas a Mooney viscosity substantially less than 200 when tested at 180"F.

11. A process of reclaiming-scrap containing elastic polychloroprene which comprises heating the same while in a sub-divided condition at an elevated temperature in the presence of material from the group consisting oi sugars and starches and for a time sufiicient to reduce the elastic, polychloroprene to a plastic state where it has a Mooney viscosity substantially less than 200 when.

elastic polychloroprene to a plastic state whereit has a Mooney viscosity substantiallyless than 200 when tested at 180 F.

13. A process of reclaiming scrap containing elastic polychloroprene which comprises heating the same while in a sub-divided condition at an elevated temperature in the presence of a discocharose and for a time sufficient to reduce the elastic polychloroprene to a plastic state where it has a Mooneyviscosity substantially less than 200 when tested at 180 F.

. 14. A process of reclaiming scrap containing elastic polychloroprene which comprises heating .the same while in a sub-divided condition at an elevated temperature in the presence of sucrose and for a'time suflicient to reduce. the elastic polychloroprene to a plastic state where it has a 420 F. in the presence of a starch convertible to a sugar during the reclaiming operation.

9. A process of reclaiming scrap containing elastic polychloroprene which comprises heating the same while in a sub-divided condition at an elevated temperature irom about 300 F. to about 420 F. in the presence of a sugar and for a time sufllcient to reduce the elastic polychloroprene to Mooney viscosity substantially'less than 200 when tested at 180F. v

15. Aprocess of reclaiming scrap containing elastic polychloroprene which comprlsesheatin the same while in a sub-divided condition at an elevated temperature in the presence of a monosaccharose and for a time suflicient' to reduce the elastic polychloropreneto a plastic state where it has a Mooney viscosity substantially less than 200 when tested at 180 F. A

'16. A process 01' reclaiming scrap containing elastic polychloroprene which comprises heatin a the same while in a sub-divided'condition at an elevated temperature in the presence of glucose and for a time suflicient to reduce the elastic polychloroprene to a plastic state whereit has a Mooney viscosity substantially less than 200 when tested at 180 F. r I

- 17. A process oi reclaiming scrap containing elastic polychloroprene which comprises heating the same while in a sub-divided condition at an elevated temperature in the presence of a starch and for a time sufllcient to reduce the elastic polychloroprene to a plastic state where it has a Mooney viscosity substantially less than 200 when tested at 180 F.

' WALTER G. KIRBY.

LEO E. STEINLE. 

